Method for forming multilevel interconnections in a semiconductor device

ABSTRACT

The present invention provides a novel method for forming multilevel interconnections in a semiconductor device. A silicon oxide film is formed on a semiconductor substrate. A first photo-resist film pattern is formed on the first silicon oxide film. The surface of the silicon oxide film covered with the photo-resist film pattern is exposed to a super-saturated hydrosilicofluoric acid solution to selectively deposit a first fluoro-containing silicon oxide film on the silicon oxide film by use of the first photo-resist film pattern as a mask. The first photo-resist film pattern is removed, thereby resulting in first grooves in the fluoro-containing silicon oxide film. First interconnections are formed within the first grooves. An inter-layer insulator is formed on an entire surface of the device and then subjected to a dry etching and a photolithography to form via holes in the inter-layer insulator. Conductive films are selectively formed in the via holes. A second photo-resist film pattern is selectively formed to cover the conductive films within the via holes. The entire surface of the device covered with the second photo-resist film pattern is exposed to a super-saturated hydrosilicofluoric acid solution to selectively deposit a second fluoro-containing silicon oxide film on the inter-layer insulator by use of the second photo-resist film pattern as a mask. The second photo-resist film pattern is removed, thereby resulting in second grooves in the second fluoro-containing silicon oxide film. Second interconnections are formed within the second grooves.

BACKGROUND OF THE INVENTION

The present invention relates to a method for forming multilevelinterconnections in a semiconductor device.

In order to increase the density of integration of the semiconductordevice, scaling down of the interconnections and increase in the numberof levels thereof are necessary. Surface planarization of an inter-layerinsulator is essential to obtain the scaling down of theinterconnections. The accuracy of the scale of the interconnectionsformed on the inter-layer insulator largely depends upon the degree ofthe surface planarization of the inter-layer insulator. The increase inthe number of the interconnection level enlarges a difference in level,or a height of the step, of the upper interconnection. If the differencein level of the upper interconnection is beyond the depth of focus inthe photo-lithography, then the scale of the interconnection isdifferent between the upper and lower parts bounded by the step. Inorder to improve the accuracy of the size of the interconnections, it isessential to reduce the step as much as possible.

In the prior art, the following forming process for the inter-layerinsulator is often used. A first silicon oxide film is deposited by aplasma chemical vapor deposition method. A spin-on-glass film is formedon the first silicon oxide film in order to obtain a planarized surface.A second silicon oxide film is deposited on the spin-on-glass film bythe plasma chemical vapor deposition method. The planarization methodusing an SOG film is effective to planarize a portion at which manynarrow interconnections are concentrated. In this case, the SOG film isformed as thin over narrow interconnections and is formed as thick overwide interconnections. As a result, it is difficult to completelyplanarize an entire surface of a chip, thereby causing the variation insize of interconnections formed on the inter-layer insulator. This meansthat it is difficult to form fine interconnections.

The requirement for completely planarizing the inter-layer insulator hasbeen on the increase. In order to facilitate the planarization, it iseffective to provide a silicon oxide film with grooves which receiveinterconnections being made of tungsten. This technique is disclosed inVLSI Multilevel Interconnection Conference Proceedings, June 1992 pp.22-28. The tungsten film is immersed in a contact portion of 64 MbitDRAM. A first interconnection layer comprises a tungsten film which isimmersed in an interconnection groove of the silicon oxide film. Asecond interconnection layer comprises a lamination structure of analuminum film and a tungsten film. Detail descriptions of the abovetechnique will be described below with reference to FIGS. 1A-1H.

As illustrated in FIG. 1A, a first insulating film 2, which is made ofsilicon oxide, is formed on a silicon substrate 1. A second insulatingfilm 4, which is made of silicon oxide film, is formed on the firstinsulating film 2.

As illustrated in FIG. 1B, a photo-resist film 27 is applied on thesecond insulating film 4 and then patterned to form a photoresistpattern 27.

As illustrated in FIG. 1C, the second insulating film is subjected to areactive ion etching using fluorine gas to form first interconnectiongrooves 5 in the second insulating film 4.

As illustrated in FIG. 1D, a titanium film 6-1 is formed by sputteringon the side walls and the bottom of each of the first interconnectiongrooves 5 and on the top of the second insulating film 4. A titaniumnitride film 7-1 is formed by sputtering on the titanium film 6-1. Atungsten film 8-1 is grown on an entire surface of the titanium nitridefilm 7-1 by a chemical vapor phase deposition method using WF₆ gas andSiH₄ gas wherein SiH₄ is reduced. As a result, the first interconnectiongrooves 5 are filled with the tungsten film 8-1 and the top of thetitanium nitride film 7-1 is completely immersed within the tungstenfilm 8-1.

As illustrated in FIG. 1E, the tungsten film 8-1, the titanium nitridefilm 7-1 and the titanium film 6-1 are selectively removed by achemical/mechanical polishing so that the tungsten film 8-1, thetitanium nitride film 7-1 and the titanium film 6-1 remain only withinthe first interconnection grooves 5. As a result, first interconnections9-1, which comprises the titanium film 6-1, the titanium nitride film7-1 and the tungsten film 8-1, are formed within the firstinterconnection grooves 5.

As illustrated in FIG. 1F, a second insulating film 13, which is made ofsilicon oxide, is formed on the level surface of the device, wherein thesecond insulating film 13 acts as an inter-layer insulator. Via holes 15are selectively formed in the second insulating film 13 by a combinationof photo-lithography and reactive ion-etching. The via holes 15 arepositioned over the remaining tungsten film 8-1 within the firstinterconnection grooves 5. The top of the first interconnections 9-1 arecovered by the second insulating film 13.

As illustrated in FIG. 1 G, a titanium film 6-2 is formed by sputteringon the side walls and the bottom of each of the via holes 15 and on thetop of the second insulating film 13. A titanium nitride film 7-2 isformed by sputtering on the titanium film 6-2. A tungsten film 8-2 isgrown on an entire surface of the titanium nitride film 7-2 by achemical vapor phase deposition method using WF₆ gas and SiH₄ gas,wherein SiH₄ is reduced. As a result, the via holes 15 are filled withthe tungsten film 8-2 and the top of the titanium nitride film 7-2 iscompletely immersed within the tungsten film 8-2. The tungsten film 8-2,the titanium nitride film 7-2 and the titanium film 6-2 are selectivelyremoved by a chemical/mechanical polishing so that the tungsten film8-2, the titanium nitride film 7-2 and the titanium film 6-2 remain onlywithin the via holes 15. As a result, the contacts 9-2, which comprisesthe titanium film 6-2 and the titanium nitride film 7-2, are formedwithin the via holes 15.

As illustrated in FIG. 1H, an insulating film 16, which is made ofsilicon oxide, is formed on the surface of the device. A photo-resistfilm, which is not illustrated, is applied on the insulating film 16 andthen patterned to form a photoresist pattern, which is not illustrated.The insulating film 16 is subjected to a reactive ion etching usingfluorine gas to form second interconnection grooves 18 in the insulatingfilm 16. A titanium film 20 is formed by sputtering on the side wallsand the bottom of each of the second interconnection grooves 18 and onthe top of the insulating film 18. An aluminum film 21 is formed bysputtering on the titanium film 20 within the second interconnectiongrooves 18. A tungsten nitride film 22 is formed on the aluminum film 21within the interconnection grooves 18. A tungsten film 23 is grown on anentire surface of the device by a chemical vapor phase deposition methodusing WF₆ gas and SiH₄ gas, wherein SiH₄ is reduced. As a result, thesecond interconnection grooves 18 are completely filled with thetungsten film 23. The tungsten film 23 are selectively removed by achemical/mechanical polishing so that the tungsten film 23, the tungstenuntried film 22, the aluminum film 21 and the titanium film 20 remainonly within the second interconnection grooves 18. As a result, secondinterconnections are formed within the second interconnection grooves18. Each of the interconnections comprises the tungsten film 23, thetungsten nitride film 22, the aluminum film 21 and the titanium film 20.

The above conventional method for forming the multilevelinterconnections has the following disadvantages. As described above,the interconnection grooves for receiving the interconnections areformed by subjecting the silicon oxide film 4 to the reactiveion-etchinlg. The silicon oxide film 4 overlays the silicon oxide film2. The silicon oxide film 4 has a not large selective ratio in reactiveion-etching to the silicon oxide film 2. Thus, the etching rate of thesilicon oxide film 4 is not much larger than the etching ratio of thesilicon oxide film 2. For that reason, it is difficult to preciselycontrol the etching depth. The reactive ion-etching depends on thepattern due to micro-loading effect. For example, the etching depth isvaried by the variation in the width of the interconnection groove. Thedepth of the interconnection groove corresponds to the thickness of theinterconnections. When the depth of the interconnection groove has avariation, this means that the interconnection thickness also has avariation, thereby resulting in deterioration of the reliability of theinterconnections.

There is another conventional method for forming multilevelinterconnections, which will hereinafter be described with reference toFIGS. 2A-2E. In order to form the multilevel interconnections by both aliquid phase growth of a silicon oxide film and a non-electro-plating.This technique is the same as disclosed in the Japanese laid-open patentapplication No. 4-290249. The process for forming the multilevelinterconnections are as follows.

As illustrated in FIG. 2A, a silicon oxide film 2 is formed on a siliconsubstrate 1. A copper film 24, having a thickness of 100 nanometers, isformed on the silicon oxide film 2 by sputtering.

As illustrated in FIG. 2B, a photo-resist film is applied on the copperfilm 24 and then pattered to form a first photo-resist pattern 3. Thecopper film 24 is selectively etched by using the first photo-resistpattern 3 as a mask. A fluoro-containing silicon oxide film 4 isselectively grown by a liquid phase growth method using the firstphoto-resist pattern 3 as a mask, so that the fluoro-containing siliconoxide film 4 is formed in apertures defined by the first photo-resistpattern 3.

As illustrated in FIG. 2C, the first photo-resist pattern 3 is removed.A first copper plating film 25 is selectively formed by anon-electro-plating method on the copper film 24 in apertures defined bythe fluoro-containing silicon oxide film 4.

As illustrated in FIG. 2D, a photo-resist film is applied on the copperfilm 24 and then pattered to form a second photo-resist pattern 11 on apredetermined part of the first copper plating film 25. Afluoro-containing silicon oxide film 13A is selectively grown by aliquid phase growth method using the second photo-resist pattern 11 as amask, so that the fluoro containing silicon oxide film 13A is formed inapertures defined by the second photo-resist pattern 11.

As illustrated in FIG. 2E, the second photo-resist pattern 11 isremoved. A second copper plating film 26 is selectively formed by anon-electro-plating method on the first copper plating film 25 inapertures defined by the fluoro-containing silicon oxide film 13A.

The above method for forming the interconnections has the followingdisadvantages. As described above, the non-electro-plating of a metal isused to fill the grooves and the holes with the metal. The metal has tobe selected from limited groups, such as gold, copper and nickel,suitable for the metal plating. It is difficult to form theinterconnections by use of the sputtering and the chemical vapordeposition. In order to form the silicon oxide film, there has to beused an H₂ SiF₆ liquid in which HF is included. Even when a boric acidis added to cause a supersaturation state, HF dissociates by extractingsilicon oxide. For this reason, it is impossible to use metals, such asaluminum, which are soluble to HF. Copper tends to be oxidized. In theplating method using a liquid, the copper surface under the via holetends to be oxidized. The oxidized surface of the copper film acts as aninsulator, whereby an electrical connection between the first and secondinterconnections can not be obtained.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a novelmethod for forming interconnections free from any disadvantages asdescribed above.

It is a further object of the present invention to provide a novelmethod for forming interconnections, which permits variable materials tobe used for the interconnections.

It is a further more object of the present invention to provide a novelmethod for forming interconnections with a uniform thickness.

It is a moreover object of the present invention to provide a novelmethod for forming multilevel interconnection structure with a highreliability.

It is a still further object of the present invention to provide a novelmethod for forming multilevel interconnections which are electricallyconnected to each other.

It is yet a further object of the present invention to provide a novelmethod for forming multilevel fine interconnections being planarlized.

The above and other objects, features and advantages of the presentinvention will be apparent from the following descriptions.

The present invention provides a novel method for formingl multilevelinterconnections in a semiconductor device. A silicon oxide film isformed on a semiconductor substrate. A first photo-resist film patternis formed on the first silicon oxide film. The surface of the siliconoxide film covered with the photo-resist film pattern is exposed to asuper-saturated hydrosilicofluoric acid solution to selectively deposita first fluoro-containing silicon oxide film on the silicon oxide filmby use of the first photo-resist film pattern as a mask. The firstphoto-resist film pattern is removed, thereby resulting in first groovesin the fluoro-containing silicon oxide film. First interconnections areformed within the first grooves. An inter-layer insulator is formed onan entire surface of the device and then subjected to a dry etching anda photolithography to form via holes in the inter-layer insulator.Conductive films are selectively formed in the via holes. A secondphoto-resist film pattern is selectively formed to cover the conductivefilms within the via holes. The entire surface of the device coveredwith the second photo-resist film pattern is exposed to asuper-saturated hydrosilicofluoric acid solution to selectively deposita second fluoro-containing silicon oxide film on the inter-layerinsulator by use of the second photo-resist film pattern as a mask. Thesecond photo-resist film pattern is removed, thereby resulting in secondgrooves in the second fluoro-containing silicon oxide film. Secondinterconnections are formed within the second grooves.

As modifications, the following process for forming the inter-layerinsulator is available. A silicon oxide base film is deposited on anentire surface of the device. A second photo-resist film pattern isselectively formed on the silicon oxide base film to overlay only thefirst interconnections. The entire surface of the device, covered withthe second photo-resist film pattern, is exposed to a super-saturatedhiydrosilicofluoric acid solution to selectively deposit afluoro-containing silicon oxide inter-layer insulator film on theinter-layer insulator by use of the second photo-resist film pattern asa mask. The second photo-resist film pattern is removed, therebyresulting in apertures in the fluoro-containing silicon oxideinter-layer insulator film. The silicon oxide base film shown throughthe apertures is removed by the reactive ion-etching so as to form viaholes in the fluoro containing silicon oxide inter-layer insulator film.A selective chemical vapor deposition method is available to selectivelyform metal films such as tungsten films within the via holes. Thefollowing processes are also available for forming metal films such astungsten films within the via holes. A metal film is deposited on anentire surface of the device and then subjected to either a dry etchingor a chemical/mechanical polishing to have the metal film partiallyremain in the via holes.

As further modifications, the silicon oxide film may contain at leastone of phosphorus, boron and germanium. Such film may be formed byeither a sputtering method or a chemical vapor deposition method. Theinterconnections may be made of a conductive material which includes atleast one of titanium nitride, tungsten, molybdenum, gold, silver,copper, silicon, aluminum, titanium, titanium-containing silicon. Suchconductive film may be formed by a chemical vapor deposition method or asputtering method.

The super-saturated hydrosilicofluoric acid solution may be prepared byheating a hydrosilicofluoric solution. The super-saturatedhydrosilicofluoric acid solution may also be prepared by dissolvingaluminum into a hydrosilicofluoric solution. The super-saturatedhydrosilicofluoric acid solution may be prepared by adding either aboric acid solution or water into a hydrosilicofluoric solution.

As described above, the interconnection grooves are formed by aselective growth of the fluoro-containing silicon oxide film withoutusing a reactive ion-etching process. This means that theinterconnection grooves are free from any variation in its size due toany variation in the size of a photoresist pattern.

When the inter-layer insulator is formed, the first interconnectionswhich underlying the inter-layer insulator are not exposed to thesupersaturated hydrosilicofluoric acid solution so that the firstinterconnections are free from any corrosion.

When the second fluoro-containing silicon oxide film which overlays theinter-layer insulator is formed, the conductive films in the via holesof the inter-layer insulator are not exposed to the super-saturatedhydrosilicofluoric acid solution so that the conductive films are freefrom any corrosion.

The groves and the via holes are filled with the conductive material toobtain level surfaces for facilitating the planarization.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Preferred embodiments of the present invention will be described indetail with reference to the accompanying drawings.

FIGS. 1A-1H are cross sectional elevation views illustrative of thesemiconductor device with multilevel interconnections involved in theconventional fabrication method.

FIGS. 2A-2E are cross sectional elevation views illustrative of thesemiconductor device with multilevel interconnections involved in theother conventional fabrication method.

FIGS. 3A-3N are cross sectional elevation views illustrative of asemiconductor device with multilevel interconnections involved in anovel fabrication method in a first embodiment according to the presentinvention.

FIGS. 4A-4J are cross sectional elevation views illustrative of asemiconductor device with multilevel interconnections involved in anovel fabrication method in a second embodiment according to the presentinvention.

FIGS. 5A-5K are cross sectional elevation views illustrative of asemiconductor device with multilevel interconnections involved in anovel fabrication method in a third embodiment according to the presentinvention.

FIGS. 6A-6H are cross sectional elevation views illustrative of asemiconductor device with multilevel interconnections involved in anovel fabrication method in a fourth embodiment according to the presentinvention.

PREFERRED EMBODIMENTS

A first embodiment according to the present invention will be describedwith reference to FIGS. 3A-3N, wherein a novel method for formingmultilevel interconnections in a semiconductor device is provided.

As illustrated in FIG. 3A, a first insulating film 2, being made ofsilicon oxide and having a thickness of 1 micrometer, is formed as afirst insulator on a silicon substrate 1 by a plasma chemical vapordeposition method. A photo-resist is applied on the silicon oxide film 2and then patterned by photo-lithography to form a photo-resist pattern3A on the first insulating film 2.

As illustrated in FIG. 3B, a second insulating film 4A, being made offluoro-containing silicon oxide and having a thickness of 0.8micrometers, is grown on the first insulating film 2 by using thephoto-resist pattern 3A as a mask. The growth of the fluoro-containingsilicon oxide film 4A is achieved by a liquid phase growth which uses asuper-saturated hydrosilicofluoric acid solution, wherein thehydrosilicofluoric acid in the solution is maintained in super-saturatedstate by immersing and dissolving an aluminum piece in an aqueoussolution which includes a hydrosilicofluoric acid at a concentration ofabout 40% by weight. The reaction of hydrosilicofluoric acid withaluminum is expressed by the following formulae.

    H.sub.2 SiF.sub.6 +2H.sub.2 O→6HF+SiO.sub.2         (1)

    Al.sup.3+ +3HF →AlF.sub.3 +3H.sup.+                 (2)

The above matter is disclosed in the Japanese laid-open patentapplication No. 62-20876. The reaction of hydrosilicofluoric acid withaluminum, which is expressed by the above formulae (1) and (2), iscaused by adding aluminum into the hydrosilicofluoric acid solution. Thechemical equilibrium expressed in the left hand term is broken, therebyresulting in an extraction of fluoro-containing silicon oxide so thatthe fluoro-containing silicon oxide film 4A, which has Si-F bonding, isdeposited on the silicon oxide film 2. During the deposition of thefluoro-containing silicon oxide film 4A, the hydrosilicofluoric acidsolution is maintained at a temperature of 35° C. so that the solubilityof aluminum to 1 liter of hydrosilicofluoric acid solution is set atapproximately 0.5 g/hour, thereby resulting in a fluoro-containingsilicon oxide film deposition rate being in the range of 80 nanometersto 100 nanometers.

As illustrated in FIG. 3C, only the first photo-resist pattern 3A havingapertures, within which the fluoro-containing silicon oxide film 4A isformed, is removed by a peeling liquid so that first interconnectiongrooves 5A defined by the fluoro-containing silicon oxide film 4A areformed.

As illustrated in FIG. 3D, the substrate is introduced into a sputteringapparatus and then a vacuum of 1×10⁻⁵ Pa is created. The substrate issubjected to an etching using an argon gas with a pressure of 0.7 Pa toremove a spontaneous oxide film from the surface of the substrate. Atitanium film 6-1 with a thickness of approximately 50 nanometers isdeposited on an entire surface of the device by a sputtering method. Atitanium nitride film 7-1 with a thickness of approximately 100nanometers is deposited on the titanium film 6-1 by a sputtering method.An aluminum film 8-1 with a thickness of 700 nanometers is formed on thetitanium nitride film 7-1 by a chemical vapor deposition, whereindimethylalminumliydride AlH(CH₃)₂ is vaporized by a bubbling method witha carrier gas of hydrogen at a temperature of 30° C. and then introducedinto a reaction chamber. The flow rate of hydrogen gas used in thebubbling method is controlled at 250 sccm. The pressure of the reactionchamber is maintained at 130 Pa. The temperature of the substrate ismaintained at 250° C. The deposition rate of aluminum is approximately0.4 micrometers/min.

As illustrated in FIG. 3E, the aluminum film 8-1, the titanium nitridefilm 7-1 and the titanium film 6-1 are selectively removed by achemical/mechanical polishing to leave the aluminum film 8-1, thetitanium nitride film 7-1 and the titanium film 6-1 only within thefirst interconnection grooves 5A. As a result, the firstinterconnections, each of which comprises the aluminum film 8-1, thetitanium nitride film 7-1 and the titanium film 6-1, are formed in thefirst interconnection grooves 5A. The polishing is carried out by usingan acid polishing agent with a pH value of 2.5 where silicon oxideparticles with a diameter of approximately 30 nanometers are dispersedin a pure water. A rotational speed of a polishing pad is maintained at50 times/min. A rotational speed of a polishing head is also maintainedat 50 times/min. The polishing agent is added at a rate of 75 cc/min.The polishing rate is approximately 0.4 micrometers/min.

As illustrated in FIG. 3F, a silicon oxide base film 10 with a thicknessof approximately 100 nanometers is formed on an entire surface of thedevice by a plasma chemical vapor deposition. A second photo-resist filmis applied on an entire surface of the silicon oxide base film 10 andthen patterned to form a second photo-resist pattern 11A whichpositioned over the aluminum film 8-1 within the first interconnectiongrooves.

As illustrated in FIG. 3G, a second fluoro-containing silicon oxide film12 with a thickness of 0.8 micrometers is grown on the silicon oxidebase film 10 by using the second photo-resist pattern 11A as a mask. Thegrowth of the fluoro-containing silicon oxide film 12 is achieved by aliquid phase growth which uses a super-saturated hydrosilicofluoric acidsolution, wherein the hydrosilicofluoric acid in the solution ismaintained in supersaturated state by immersing and dissolving analuminum piece in an aqueous solution which includes ahydrosilicofluoric acid at a concentration of about 40% by weight. Thereaction of hydrosilicofluoric acid with aluminum is expressed by theforegoing formula (1) and (2). The reactions of hydrosilicofluoric acidwith aluminum, which are expressed by the above formulae (1) and (2),are caused by adding aluminum into the hydrosilicofluoric acid solution.The chemical equilibrium expressed in the left hand term is broken,thereby resulting in an extraction of fluoro containing silicon oxide sothat the second fluoro-containing silicon oxide film 12, which has Si-Fbonding, is deposited. During the deposition of the fluoro-containingsilicon oxide film 12, the hydrosilicofluoric acid solution ismaintained at a temperature of 35° C. so that the solubility of aluminumto 1 liter of hydrosilicofluoric acid solution is set at approximately0.5 g/hour, thereby resulting in a fluoro-containing silicon oxide filmdeposition rate being in the range of 80 nanometers to 100 nanometers.The second photo-resist pattern 11 A, having apertures within which thefluoro-containing silicon oxide film 12 is formed, is removed by apeeling liquid so that openings 14 are formed in the fluoro-containingsilicon oxide film 12.

As illustrated in FIG. 3H, the silicon oxide base film 10 under theopenings 14 is selectively removed by a reactive dry etching which usesCF₄ gas to form via holes 15A over the titanium films 8-1 within thefirst interconnection grooves 5A. The reactive dry etching is carriedout by using a parallel plate type apparatus usable for batchtreatments. The flow rate of CF₄ gas is maintained at 100 sccm. Thepressure of the reaction chamber is set at 10 Pa. The substratetemperature is maintained at 20° C. A power of 1 kW with a frequency of13.56 MHz is applied. The etching rate of approximately 40nanometers/min. is obtained. By the etch back process, the thickness ofthe fluoro-containing silicon oxide film 12 is reduced to approximately0.65 micrometers. The fluoro-containing silicon oxide film 12 and thesilicon oxide base film 10 constitute a third insulator 13B.

As illustrated in FIG. 31, a titanium film 6-2 with a thickness of 50nanometers is deposited on an entire surface of the device by asputtering method. A titanium nitride film 7-2 with a thickness of 100nanometers is deposited on the titanium film 6-2 by a sputtering method.An aluminum film 8-2 with a thickness of approximately 0.7 micrometersis formed on the titanium nitride film 7-2 by a thermal chemical vaporphase deposition. wherein dimethylalminumhydride AlH(CH₃)₂ is vaporizedby a bubbling method with a carrier gas of hydrogen at a temperature of30° C. and then introduced into a reaction chamber. The flow rate ofhydrogen gas used in the hubbling method is controlled at 250 sccm. Thepressure of the reaction chamber is maintained at 130 Pa. Thetemperature of the substrate is maintained at 250° C. The depositionrate of aluminums is approximately 0.4 micrometers/mn.

As illustrated in FIG. 3J, the aluminum film 8-2, the titanium nitridefilm 7-2 and the titanium film 6-2 are selectively removed by achemical/mechanical polishing to leave the aluminum film 8-2, thetitanium nitride film 7-2 and the titanium film 6-2 only within the viaholes 15A. As a result, the conductive films, each of which comprisesthe aluminum film 8-2, the titanium nitride film 7-2 and the titaniumfilm 6-2, are formed in the via holes 15A. The polishing is carried outby using an acid polishing agent with a pH value of 2.5 where siliconoxide particles with a diameter of approximately 30 nanometers aredispersed in a pure water. A rotational speed of a polishing pad ismaintained at 50 times/min. A rotational speed of a polishing head isalso maintained at 50 times/min. The polishing agent is added at a rateof 75 cc/min. The polishing rate is approximately 0.4 micrometers/min.

As illustrated in FIG. 3K, a third photo-resist film is applied on anentire surface of the device and then patterned to selectively form athird photo-resist pattern 17. A third fluoro-containing silicon oxidefilm 16A with a thickness of 0.8 micrometers is grown on the secondfluoro-containing silicon oxide film by using the third photo-resistpattern 17 as a mask. The growth of the fluoro-containing silicon oxidefilm 16A is achieved by a liquid phase growth which uses asuper-saturated hydrosilicofluoric acid solution, wherein thehydrosilicofluoric acid in the solution is maintained in super-saturatedstate by immersing and dissolving an aluminum piece in an aqueoussolution which includes a hydrosilicofluoric acid at a concentration ofabout 40% by weight. The reactions of hydrosilicofluoric acid withaluminum are expressed by the foregoing formulae (1) and (2). Thereactions of hydrosilicofluoric acid with aluminum, which are expressedby the above formulae (1) and (2), are caused by adding aluminum intothe hydrosilicofluoric acid solution. The chemical equilibrium expressedin the left hand term is broken, thereby resulting in an extraction offluoro-containing silicon oxide so that the third fluoro-containingsilicon oxide film 16A, which has Si-F bonding, is deposited. During thedeposition of the fluoro-containing silicon oxide film 16A, thehydrosilicofluoric acid solution is maintained at a temperature of 35°C. so that the solubility of aluminum to 1 liter of hydrosilicofluoricacid solution is set at approximately 0.5 g/hour, thereby resulting in afluoro-containing silicon oxide film deposition rate being in the rangeof 80 nanometers to 100 nanometers.

As illustrated in FIG. 3L, the third photo-resist pattern 17, havingapertures within which the fluoro-containing silicon oxide film 12 isformed, is removed by a peeling liquid so that third interconnectiongrooves 1 8A are formed in the third fluoro-containing silicon oxidefilm 16A.

As illustrated in FIG. 3M, a titanium film 6-3 with a thickness of 50nanometers is deposited on an entire surface of the device by asputtering method. A titanium nitride film 7-3 with a thickness of 100nanometers is deposited on the titanium film 6-3 by a sputtering method.An aluminum film 8-3 with a thickness of approximately 0.7 micrometersis formed on the titanium nitride film 7-3 by a thermal chemical vaporphase deposition, wherein dimethylalminumhydride AlH(CH₃)₂ is vaporizedby a bubbling method with a carrier gas of hydrogen at a temperature of30° C. and then introduced into a reaction chamber. The flow rate ofhydrogen gas used in the bubbling method is controlled at 250 sccm. Thepressure of the reaction chamber is maintained at 130 Pa. Thetemperature of the substrate is maintained at 250° C. The depositionrate of aluminum is approximately 0.4 micrometers/min.

As illustrated in FIG. 3N, the aluminum film 8-3, the titanium nitridefilm 7-3 and the titanium film 6-3 are selectively removed by achemical/mechanical polishing to leave the aluminum film 8-3, thetitanium nitride film 7-3 and the titanium film 6-3 only within thethird interconnection grooves 18A. As a result, the secondinterconnections 9-3a, each of which comprises the aluminum film 8-3,the titanium nitride film 7-3 and the titanium film 6-3, are formed inthe second interconnection grooves 5A. The polishing is carried out byusing an acid polishing agent with apH value of 2.5 where silicon oxideparticles with a diameter of approximately 30 nanometers are dispersedin a pure water. A rotational speed of a polishing pad is maintained at50 times/min. A rotational speed of a polishing head is also maintainedat 50 times/min. The polishing agent is added at a rate of 75 cc/min.The polishing rate is approximately 0.4 micrometers/min.

The two level interconnection structure is fabricated. The surface ofthe inter-layer insulator between the two level interconnection layersare leveled. A sample is formed by use of the above technique, whereinten thousand via holes are connected in series to each other. A diameterof the via holes is 0.6 micrometers. Each via hole has a resistance ofapproximately 0.3 Ω. The yield is 95%.

According to the above method, the silicon oxide base film is formed tocover the first interconnections before the surface of the device isexposed to the super-saturated hydrosilicofluoric acid solution so thatthe first interconnections are free from any corrosion caused by thesuper-saturated hydrosilicofluoric acid solution. The conductive filmwithin the via holes are also free from any corrosion caused by thesuper-saturated hydrosilicofluoric acid solution as being covered withthe photo-resist film. The combination of the chemical/mechanicalpolishing and subsequent liquid phase growth allows the inter-layerinsulator to have a level surface.

A second embodiment according to the present invention will be describedwith reference to FIGS. 4A-4J, wherein a novel method for formingmultilevel interconnections in a semiconductor device is provided.

As illustrated in FIG. 4A, a first insulating film 2, being made ofsilicon oxide and having a thickness of 1 micrometer, is formed as afirst insulator on a silicon substrate 1 by a plasma chemical vapordeposition method. A photo-resist is applied on the silicon oxide film 2and then patterned by photo-lithography to form a photo-resist pattern3A on the first insulating film 2.

As illustrated in FIG. 4B, a second insulating film 4A, being made offluoro-containing silicon oxide and having a thickness of 0.8micrometers, is grown on the first insulating film 2 by using thephoto-resist pattern 3A as a mask. The growth of the fluoro-containingsilicon oxide film 4A is achieved by a liquid phase growth which uses asuper-saturated hydrosilicofluoric acid solution, wherein thehydrosilicofluoric acid in the solution is maintained in super-saturatedstate by immersing and dissolving an aluminum piece in an aqueoussolution which includes a hydrosilicofluoric acid at a concentration ofabout 40% by weight. The reaction of hydrosilicofluoric acid withaluminum is expressed by the following formulae.

    H.sub.2 SiF.sub.6 +2H.sub.2 O→6HF+SiO.sub.2         (1)

    Al.sup.3+ +3HF→AlF.sub.3 +3H.sup.+                  (2)

The above matter is disclosed in the Japanese laid-open patentapplication No. 62-20876. The reaction of hydrosilicofluoric acid withaluminum, which is expressed by the above formula (1) and (2), is causedby adding aluminum into the hydrosilicofluoric acid solution. Thechemical equilibrium expressed in the left hand term is broken, therebyresulting in an extraction of fluoro-containing silicon oxide so thatthe fluoro-containing silicon oxide film 4A, which has Si-F bonding, isdeposited on the silicon oxide film 2. During the deposition of thefluoro-containing silicon oxide film 4A, the hydrosilicofluoric acidsolution is maintained at a temperature of 35° C. so that the solubilityof aluminum to 1 liter of hydrosilicofluoric acid solution is set atapproximately 0.5 g/hour, thereby resulting in a fluoro-containingsilicon oxide film deposition rate being in the range of 80 nanometersto 100 nanometers.

As illustrated in FIG. 4C, only the first photo-resist pattern 3A havingapertures, within which the fluoro-containing silicon oxide film 4A isformed, is removed by a peeling liquid so that first interconnectiongrooves 5A defined by the fluoro-containing silicon oxide film 4A areformed.

As illustrated in FIG. 4D, the substrate is introduced into a sputteringapparatus and then a vacuum of 1×10⁻⁵ Pa is created. The substrate issubjected to an etching using an argon gas with a pressure of 0.7 Pa toremove a spontaneous oxide film from the surface of the substrate. Atitanium film 6-1 with a thickness of approximately 50 nanometers isdeposited on an entire surface of the device by a sputtering method. Atitanium nitride film 7-1 with a thickness of approximately 100nanometers is deposited on the titanium film 6-1 by a sputtering method.An aluminum film 8-1 with a thickness of 700 nanometers is formed on thetitanium nitride film 7-1 by a chemical vapor deposition, whereindimethylalminumlhydride AlH(CH₃)₂ is vaporized by a bubbling method witha carrier gas of hydrogen at a temperature of 30° C. and then introducedinto a reaction chamber. The flow rate of hydrogen gas used in thebubbling method is controlled at 250 sccm. The pressure of the reactionchamber is maintained at 130 Pa. The temperature of the substrate ismaintained at 250° C. The deposition rate of aluminum is approximately0.4 micrometers/min.

As illustrated in FIG. 4E, the aluminum film 8-1, the titanium nitridefilm 7-1 and the titanium film 6-1 are selectively removed by achemical/mechanical polishing to leave the aluminum film 8-1, thetitanium nitride film 7-1 and the titanium film 6-1 only within thefirst interconnection grooves 5A. As a result, the firstinterconnections, each of which comprises the aluminum film 8-1, thetitanium nitride film 7-1 and the titanium film 6-1, are formed in thefirst interconnection grooves 5A. The polishing is carried out by usingan acid polishing agent with a pH value of 2.5 where silicon oxideparticles with a diameter of approximately 30 nanometers are dispersedin a pure water. A rotational speed of a polishing pad is maintained at50 times/min. A rotational speed of a polishing head is also maintainedat 50 times/min. The polishing agent is added at a rate of 75 cc/min.The polishing rate is approximately 0.4 micrometers/min.

As illustrated in FIG. 4F, a silicon oxide base film 10 with a thicknessof approximately 100 nanometers is formed on an entire surface of thedevice by a plasma chemical vapor deposition. A second photo-resist filmis applied on an entire surface of the silicon oxide base film 10 andthen patterned to form a second photo-resist pattern 1 1A whichpositioned over the aluminum film 8-1 within the first interconnectiongrooves.

As illustrated in FIG. 4G, a second fluoro-containing silicon oxide film12 with a thickness of 0.8 micrometers is grown on the silicon oxidebase film 10 by using the second photo-resist pattern 1 1A as a mask.The growth of the fluoro-containing silicon oxide film 12 is achieved bya liquid phase growth which uses a super-saturated hydrosilicofluoricacid solution, wherein the hydrosilicofluoric acid in the solution ismaintained in supersaturated state by immersing and dissolving analuminum piece in an aqueous solution which includes ahydrosilicofluoric acid at a concentration of about 40% by weight. Thereaction of hydrosilicofluoric acid with aluminum is expressed by theforegoing formulae (1) and (2). The reactions of hydrosilicofluoric acidwith aluminum, which are expressed by the above formulae (1) and (2),are caused by adding aluminum into the hydrosilicofluoric acid solution.The chemical equilibrium expressed in the left hand term is broken,thereby resulting in an extraction of flurocontaining silicon oxide sothat the second fluoro-containing silicon oxide film 12, which has Si-Fbonding, is deposited. During the deposition of the fluoro-containingsilicon oxide film 12, the hydrosilicofluoric acid solution ismaintained at a temperature of 35° C. so that the solubility of aluminumto 1 liter of hydrosilicofluoric acid solution is set at approximately0.5 g/hour, thereby resulting in a fluoro-containing silicon oxide filmdeposition rate being in the range of 80 nanometers to 100 nanometers.The second photoresist pattern 1 A, having apertures within which thefluoro-containing silicon oxide film 12 is formed, is removed by apeeling liquid so that openings 14 are formed in the fluoro-containingsilicon oxide film 12.

As illustrated in FIG. 4H, the silicon oxide base film 10 tinder theopenings 14 is selectively removed by a reactive dry etching which usesCF₄ gas to form via holes 15A over the titanium films 8-1 within thefirst interconnection grooves 5A. The reactive dry etching is carriedout by using a parallel plate type apparatus usable for batchtreatments. The flow rate of CF₄ gas is maintained at 100 sccm. Thepressure of the reaction chamber is set at 10 Pa. The substratetemperature is maintained at 20° C. A power of 1 kW with a frequency of13.56 MHz is applied. The etching rate of approximately 40nanometers/min. is obtained. By the etch back process, the thickness ofthe fluoro-containing silicon oxide film 12 is reduced to approximately0.65 micrometers. The fluoro-containing silicon oxide film 12 and thesilicon oxide base film 10 constitute a third insulator 13B.

As illustrated in FIG. 41, a tungsten film 19 with a thickness ofapproximately 0.8 micrometers is selectively formed within the via holes51 A by a heat chemical vapor phase growth, in which WF₆ gas and SiH₄gas are used. The respective flow rates of WF₆ gas and SiH₄ gas are setat 20 sccm and 12 sccm. The substrate temperature is maintained at 270°C. The pressure of the reaction chamber is set at 4 Pa. The depositionrate is 0.6 micrometers/min.

As illustrated in FIG. 4J, a third photo-resist film is applied on allentire surface of the device and then patterned to selectively form athird photo-resist pattern, which is not illustrated and covers thetungsten film 19. A third fluoro-containing silicon oxide film 16A witha thickness of 0.8 micrometers is grown only the third fluoro-containingsilicon oxide film by using the third photo-resist pattern as a mask.The growth of the fluoro-containing silicon oxide film 16A is achievedby a liquid phase growth which uses a super-saturated hydrosilicofluoricacid solution, wherein the hydrosilicofluoric acid in the solution ismaintained in super-saturated state by immersing and dissolving analuminum piece in an aqueous solution which includes ahydrosilicofluoric acid at a concentration of about 40% by weight. Thereactions of hydrosilicofluoric acid with aluminum are expressed by theforegoing formulae (1) and (2). The reactions of hydrosilicofluoric acidwith aluminum, which are expressed by the above formulae (1) and (2),are caused by adding aluminum into the hydrosilicofluoric acid solution.The chemical equilibrium expressed in the left hand term is broken,thereby resulting in an extraction of fluoro-containing silicon oxide sothat the third fluoro-containing silicon oxide film 16A, which has Si-Fbonding, is deposited. During the deposition of the fluoro-containingsilicon oxide film 16A, the hydrosilicofluoric acid solution ismaintained at a temperature of 35° C. so that the solubility of aluminumto 1 liter of hydrosilicofluoric acid solution is set at approximately0.5 g/hour, thereby resulting in a fluoro-containing silicon oxide filmdeposition rate being in the range of 80 nanometers to 100 nanometers.

Subsequently, the third photo-resist pattern 17, having apertures withinwhich the fluoro-containing silicon oxide film 12 is formed, is removedby a peeling liquid so that third interconnection grooves 1 8A areformed in the third fluoro-containing silicon oxide film 1 6A.

A titanium film 6-3 with a thickness of 50 nanometers is deposited on anentire surface of the device by a sputtering method. A titanium nitridefilm 7-3 with a thickness of 100 nanometers is deposited on the titaniumfilm 6-3 by a sputtering method. An aluminum film 8-3 with a thicknessof approximately 0.7 micrometers is formed on the titanium nitride film7-3 by a thermal chemical vapor phase deposition, whereindimetlhylalminumhlydride AlH(CH₃)₂ is vaporized by a bubbling methodwith a carrier gas of hydrogen at a temperature of 30° C. and thenintroduced into a reaction chamber. The flow rate of hydrogen gas usedin the bubbling method is controlled at 250 sccm. The pressure of thereaction chamber is maintained at 130 Pa. The temperature of thesubstrate is maintained at 250° C. The deposition rate of aluminum isapproximately 0.4 micrometers/min.

The aluminum film 8-3, the titanium nitride film 7-3 and the titaniumfilm 6-3 are selectively removed by a chemical/mechanical polishing toleave the aluminum film 8-3, the titanium nitride film 7-3 and thetitanium in film 6-3 only within the third interconnection grooves 18A.As a result, the second interconnections 9-3a, each of which comprisesthe aluminum film 8-3, the titanium nitride film 7-3 and the titaniumfilm 6-3, are formed in the second interconnection grooves 5A. Thepolishing is carried out by using an acid polishing agent with a pHvalue of 2.5 where silicon oxide particles with a diameter ofapproximately 30 nanometers are dispersed in a pure water. A rotationalspeed of a polishing pad is maintained at 50 times/min. A rotationalspeed of a polishing head is also maintained at 50 times/min. Thepolishing agent is added at a rate of 75 cc/min. The polishing rate isapproximately 0.4 micrometers/min.

The two level interconnection structure is fabricated. The surface ofthe inter-layer insulator between the two level interconnection layersare leveled. A sample is formed by use of the above technique, whereinten thousand via holes are connected in series to each other. A diameterof the via holes is 0.6 micrometers. Each via hole has a resistance ofapproximately 0.8 Ω. The yield is over 93%.

According to the above method, the silicon oxide base film is formed tocover the first interconnections before the surface of the device isexposed to the super-saturated hydrosilicofluoric acid solution so thatthe first interconnections are free from any corrosion caused by thesuper-saturated hydrosilicofluoric acid solution. The tungsten filmwithin the via holes are also free from any corrosion caused by thesuper-saturated hydrosilicofluoric acid solution as being covered withthe photo-resist film. The combination of the chemical/mechanicalpolishing and subsequent liquid phase growth allows the inter-layerinsulator to have a level surface.

A third embodiment according to the present invention will be describedwith reference to FIGS. 5A-5K, wherein a novel method for formingmultilevel interconnections in a semiconductor device is provided.

As illustrated in FIG. 5A, a first insulating film 2, being made ofsilicon oxide and having a thickness of 1 micrometer, is formed as afirst insulator on a silicon substrate 1 by a plasma chemical vapordeposition method. A photo-resist is applied on the silicon oxide film 2and then patterned by photo-lithography to form a photo-resist pattern3A on the first insulating film 2.

As illustrated in FIG. 5B, a second insulating film 4A, being made offluoro-containing silicon oxide and having a thickness of 0.8micrometers, is grown on the first insulating film 2 by using thephoto-resist pattern 3A as a mask. The growth of the fluoro-containingsilicon oxide film 4A is achieved by a liquid phase growth which uses asuper-saturated hydrosilicofluoric acid solution, wherein thehydrosilicofluoric acid in the solution is maintained in super-saturatedstate by immersing and dissolving an aluminum piece in an aqueoussolution which includes a hydrosilicofluoric acid at a concentration ofabout 40% by weight. The reaction of hydrosilicofluoric acid withaluminum is expressed by the following formulae.

    H.sub.2 SiF.sub.6 +2H.sub.2 O→6HF+ISO.sub.2         (1)

    Al.sup.3+ +3HF→AlF.sub.3 +3H.sup.+                  (2)

The above matter is disclosed in the Japanese laid-open patentapplication No. 62-20876. The reaction of hydrosilicofluoric acid withaluminum, which is expressed by the above formulae (1) and (2), iscaused by adding aluminum into the hydrosilicofluoric acid solution. Thechemical equilibrium expressed in the left hand term is broken, therebyresulting in an extraction of fluoro-containing silicon oxide so thatthe fluoro-containing silicon oxide film 4A, which has Si-F bonding, isdeposited on the silicon oxide film 2. During the deposition of thefluoro-containing silicon oxide film 4A, the hydrosilicofluoric acidsolution is maintained at a temperature of 35° C. so that the solubilityof aluminum to 1 liter of hydrosilicofluoric acid solution is set atapproximately 0.5 g/hour, thereby resulting in a fluoro-containingsilicon oxide film deposition rate being in the range of 80 nanometersto 100 nanometers.

As illustrated in FIG. 5C, only the first photo-resist pattern 3A havingapertures, within which the fluoro-containing silicon oxide film 4A isformed, is removed by a peeling liquid so that first interconnectiongrooves 5A defined by the fluoro-containing silicon oxide film 4A areformed.

As illustrated in FIG. 5D, the substrate is introduced into a sputteringapparatus and then a vacuum of 1×10⁻⁵ Pa is created. The substrate issubjected to an etching using an argon gas with a pressure of 0.7 Pa toremove a spontaneous oxide film from the surface of the substrate. Atitanium film 6-1 with a thickness of approximately 50 nanometers isdeposited on an entire surface of the device by a sputtering method. Atitanium nitride film 7-1 with a thickness of approximately 100nanometers is deposited on the titanium film 6-1 by a sputtering method.An aluminum film 8-1 with a thickness of 700 nanometers is formed on thetitanium nitride film 7-1 by a chemical vapor deposition, whereindimetlhylalminumlhydride AlH(CH₃)₂ is vaporized by a hubbling methodwith a carrier gas of hydrogen at a temperature of 30° C. and thenintroduced into a reaction chamber. The flow rate of hydrogen gas usedin the bubbling method is controlled at 250 scm. The pressure of thereaction chamber is maintained at 130 Pa. The temperature of thesubstrate is maintained at 250° C. The deposition rate of aluminum isapproximately 0.4 micrometers/min.

As illustrated in FIG. 5E, the aluminum film 8-1, the titanium nitridefilm 7-1 and the titanium film 6-1 are selectively removed by achemical/mechanical polishing to leave the aluminum film 8-1, thetitanium nitride film 7-1 and the titanium film 6-1 only within thefirst interconnection grooves SA. As a result, the firstinterconnections, each of which comprises the aluminum film 8-1, thetitanium nitride film 7-1 and the titanium film 6-1, are formed in thefirst interconnection grooves 5A. The polishing is carried out by usingan acid polishing agent with a pH value of 2.5 where silicon oxideparticles with a diameter of approximately 30 nanometers are dispersedin a pure water. A rotational speed of a polishing pad is maintained at50 times/min. A rotational speed of a polishing head is also maintainedat 50 times/min. The polishing agent is added at a rate of 75 cc/min.The polishing rate is approximately 0.4 micrometers/mim.

As illustrated in FIG. 5F, a second photo-resist film is applied on anentire surface of the silicon oxide base film 10 and then patterned toform a second photo-resist pattern 11A which positioned over thealuminum film 8-1 within the first interconnection grooves.

As illustrated in FIG. 5G, a second fluoro-containing silicon oxide film12 with a thickness of 0.8 micrometers is grown on the silicon oxidebase film 10 by using the second photo-resist pattern 1 1A as a mask.The growth of the fluoro-containing silicon oxide film 12 is achieved bya liquid phase growth which uses a super-saturated hydrosilicofluoricacid solution, wherein the hydrosilicofluoric acid in the solution ismaintained in supersaturated state by immersing and dissolving analuminum piece in an aqueous solution which includes ahydrosilicofluoric acid at a concentration of about 40% by weight. Thereaction of hydrosilicofluoric acid with aluminum is expressed by theforegoing formulae (1) and (2). The reactions of hydrosilicofluoric acidwith aluminum, which are expressed by the above formulae (1) and (2),are caused by adding aluminum into the hydrosilicofluoric acid solution.The chemical equilibrium expressed in the left hand term is broken,thereby resulting in an extraction of fluoro co ntaining silicon oxideso that the second fluoro-containing silicon oxide film 12, which hasSi-F bonding, is deposited. During the deposition of thefluoro-containing silicon oxide film 11, the hydrosilicofluoric acidsolution is maintained at a temperature of 35° C. so that the solubilityof aluminum to 1 liter of hydrosilicofluoric acid solution is set atapproximately 0.5 g/hour, thereby resulting in a fluoro-containingsilicon oxide film deposition rate being in the range of 80 nanometersto 100 nanometers. The second photo-resist pattern 11 A, havingapertures within which the fluoro-containing silicon oxide film 12 isformed, is removed by a peeling liquid so that openings 14 are formed inthe fluoro-containing silicon oxide film 12.

As illustrated in FIG. 5H, a silicon oxide film 13C with a thickness of0.8 micrometers is formed on an entire surface of the device by a plasmachemical vapor phase growth. Via holes 15B are formed in the siliconoxide film 13C by a photo-lithography and a subsequent selectivereactive ion-etching which uses a CHF₃ gas.

As illustrated in FIG. 51, a titanium film 6-2 with a thickness of 50nanometers is deposited on an entire surface of the device by asputtering method. A titanium nitride film 7-2 with a thickness of 100nanometers is deposited on the titanium film 6-2 by a sputtering method.A tungsten film 19A with a thickness of approximately 0.7 micrometers isformed on the titanium nitride film 7-2 by a thermal chemical vaporphase deposition. WF₆ gas and H₂ gas are used. The flow rates of WF₆ gasand H₂ gas are respectively controlled at 100 sccm and 1 slm. Thepressure of the reaction chamber is maintained at 6600 Pa. Thetemperature of the substrate is maintained at 400° C. The depositionrate of tungsten is approximately 0.3 micrometers/min.

As illustrated in FIG. 5J, the tungsten film 19-A, the titanium nitridefilm 7-2 and the titanium film 6-2 are selectively removed by achemical/mechanical polishing to leave the tungsten film 19-A, thetitanium nitride film 7-2 and the titanium film 6-2 only within the viaholes 15B. As a result, the conductive films, each of which comprisesthe tungsten film 19-A, the titanium nitride film 7-2 and the titaniumfilm 6-2, are formed in the via holes 15B. The polishing is carried outby using an acid polishing agent with a pH value of 2.5 where siliconoxide particles with a diameter of approximately 30 nanometers aredispersed in a pure water. A rotational speed of a polishing pad ismaintained at 50 times/min. A rotational speed of a polishing head isalso maintained at 50 times/min. The polishing agent is added at a rateof 75 cc/min. The polishing rate is approximately 0.3 micrometers/min.

As illustrated in FIG. 5K, a third photo-resist film is applied oil anentire surface of the device and then patterned to selectively fonm athird photo-resist pattern 17. A third fluoro-containing silicon oxidefilm 16A with a thickness of 0.8 micrometers is grown on the thirdfluoro-containing silicon oxide film by using the third photo-resistpattern 17 as a mask. The growth of the fluoro-containing silicon oxidefilm 16A is achieved by a liquid phase growth which c uses asuper-saturated hydrosilicoflloric acid solution, wherein thehydrosilicofluoric acid in the solution is maintained in super-saturatedstate by immersing and dissolving an aluminum piece in an aqueoussolution which includes a hydrosilicofluoric acid at a concentration ofabout 40% by weight. The reactions of hydrosilicofluoric acid withaluminum re expressed by the foregoing formulae (1) and (2). Thereactions of hydrosilicofluoric acid with aluminum, which are expressedby the above formula (1) and (2), are caused by adding aluminum into thehydrosilicofluoric acid solution. The chemical equilibrium expressed inthe left hand term is broken, thereby resulting in an extraction offluoro containing silicon oxide so that the third fluoro-containingsilicon oxide film 16A, which has Si-F bonding, is deposited. During thedeposition of the fluoro-containing silicon oxide film 16A, thehydrosilicofluoric acid solution is maintained at a temperature of 35°C. so that the solubility of aluminum to 1 liter of hydrosilicofluoricacid solution is set at approximately 0.5 g/hour, thereby resulting in afluoro-containing silicon oxide film deposition rate being in the rangeof 80 nanometers to 100 nanometers.

The third photo-resist pattern, having apertures within which thefluoro-containing silicon oxide film 12 is formed, is removed by apeeling liquid so that third interconnection grooves 18A are formed inthe third fluoro-containing silicon oxide film 16A. A titanium film 6-3with a thickness of 50 nanometers is deposited on an entire surface ofthe device by a sputtering method. A titanium nitride film 7-3 with athickness of 100 nanometers is deposited on the titanium film 6-3 by asputtering method. An aluminum film 8-3 with a thickness ofapproximately 0.7 micrometers is formed on the titanium nitride film 7-3by a thermal chemical vapor phase deposition, whereindimethylalminumthydride AlH(CH₃)₂ is vaporized by a bubbling method witha carrier gas of hydrogen at a temperature of 30° C. and then introducedinto a reaction chamber. The flow rate of hydrogen gas used in thehubbling method is controlled at 250 sccm. The pressure of the reactionchamber is maintained at 130 Pa. The temperature of the substrate ismaintained at 250° C. The deposition rate of aluminum is approximately0.4 micrometers/min. The aluminum film 8-3, the titanium nitride film7-3 and the titanium film 6-3 are selectively removed by achemical/mechanlical polishing to leave the aluminum film 8-3, thetitanium nitride film 7-3 and the titanium film 6-3 only within thethird interconnection grooves 18A. As a result, the secondinterconnections 9-3a, each of which comprises the aluminum film 8-3,the titanium nitride film 7-3 and the titanium film 6-3, are formed inthe second interconnection grooves SA. The polishing is carried out byusing an acid polishing agent with a pH value of 2.5 where silicon oxideparticles with a diameter of approximately 30 nanometers are dispersedin a pure water. A rotational speed of a polishing pad is maintained at50 times/min. A rotational speed of a polishing head is also maintainedat 50 times/min. The polishing agent is added at a rate of 75 cc/min.The polishing rate is approximately 0.4 micrometers/min.

The two level interconnection stricture is fabricated. The surface ofthe inter-layer insulator between tile two level interconnection layersare leveled. A sample is formed by use of the above technique, whereinten thousand via holes are connected in series to each other. A diameterof the via holes is 0.6 micrometers. Each via hole has a resistance ofapproximately 0.7 Ω. The yield is 95%.

According to the above method, the silicon oxide base film is formed tocover the first interconnections before the surface of the device isexposed to the super-saturated hydrosilicofluoric acid solution so thattile first interconnections are free from any corrosion caused by thesuper-saturated hydrosilicofluoric acid solution. The conductive filmwithin the via holes are also free from any corrosion caused by thesuper-saturated hydrosilicofluoric acid solution as being covered withthe photo-resist film. The combination of the chemical/mechanicalpolishing and subsequent liquid phase growth allows the inter-layerinsulator to have a level surface.

A fourth embodiment according to the present invention will be describedwith reference to FIGS. 6A-5H, wherein a novel method for formingmultilevel interconnections in a semiconductor device is provided.

As illustrated in FIG. 6A, a first insulating film 2, being made ofsilicon oxide and having a thickness of 1 micrometer, is formed as afirst insulator on a silicon substrate 1 by a plasma chemical vapordeposition method. A photo-resist is applied on the silicon oxide film 2and then patterned by photo-lithography to form a photo-resist pattern3A on the first insulating film 2.

As illustrated in FIG. 6B, a second insulating film 4A, being made offluoro-containing silicon oxide and having a thickness of 0.8micrometers, is grown on the first insulating film 2 by using thephoto-resist pattern 3A as a mask. The growth of the fluoro-containingsilicon oxide film 4A is achieved by a liquid phase growth which uses asuper-saturated hydrosilicofluoric acid solution, wherein thehydrosilicofluoric acid in the solution is maintained in super-saturatedstate by immersing and dissolving an aluminum piece in an aqueoussolution which includes a hydrosilicofluoric acid at a concentration ofabout 40% by weight. The reaction of hydrosilicofluoric acid withaluminum is expressed by the following formulae.

    H.sub.2 SiF.sub.6 +2H.sub.2 O→6HF+SiO.sub.2         (1)

    Al.sup.3+ +3HF→AlF.sub.3 +3H.sup.+                  (2)

The above matter is disclosed in the Japanese laid-open patentapplication No. 62-20876. The reaction of hydrosilicofluoric acid withaluminum, which is expressed by the above formula (1) and (2), is causedby adding aluminum into the hydrosilicofluoric acid solution. Thechemical equilibrium expressed in the left hand term is broken, therebyresulting in an extraction of fluoro-containing silicon oxide so thatthe fluoro-containing silicon oxide film 4A, which has Si-F bonding, isdeposited on the silicon oxide film 2. During the deposition of thefluoro-containing silicon oxide film 4A, the hydrosilicofluoric acidsolution is maintained at a temperature of 35° C. so that the solubilityof aluminum to 1 liter of hydrosilicofluoric acid solution is set atapproximately 0.5 g/hour, thereby resulting in a fluoro-containingsilicon oxide film deposition rate being in the range of 80 nanometersto 100 nanometers.

As illustrated in FIG. 6C, only the first photo-resist pattern 3A havingapertures, within which the fluoro-containing silicon oxide film 4A isformed, is removed by a peeling liquid so that first interconnectiongrooves 5A defined by the fluoro-containing silicon oxide film 4A areformed.

As illustrated in FIG. 6D, the substrate is introduced into a sputteringapparatus and then a vacuum of 1×10⁻⁵ Pa is created. The substrate issubjected to an etching using an argon gas with a pressure of 0.7 Pa toremove a spontaneous oxide film from the surface of the substrate. Atitanium film 6-1 with a thickness of approximately 50 nanometers isdeposited on an entire surface of the device by a sputtering method. Atitanium nitride film 7-1 with a thickness of approximately 100nanometers is deposited on the titanium film 6-1 by a sputtering method.An aluminum film 8-1 with a thickness of 700 nanometers is formed on thetitanium nitride film 7-1 by a chemical vapor deposition, whereindimethylalminumnhydride AlH(CH₃)₂ is vaporized by a bubbling method witha carrier gas of hydrogen at a temperature of 30° C. and then introducedinto a reaction chamber. The flow rate of hydrogen gas used in thebubbling method is controlled at 250 sccm. The pressure of the reactionchamber is maintained at 130 Pa. The temperature of the substrate ismaintained at 250° C. The deposition rate of aluminum is approximately0.4 micrometers/min.

As illustrated in FIG. 6E, the aluminum film 8-1, the titanium nitridefilm 7-1 and the titanium film 6-1 are selectively removed by achemical/mechanical polishing to leave the aluminum film 8-1, thetitanium nitride film 7-1 and the titanium film 6-1 only within thefirst interconnection grooves 5A. As a result, the firstinterconnections, each of which comprises the aluminum film 8-1, thetitanium nitride film 7-1 and the titanium film 6-1, are formed in thefirst interconnection grooves 5A. The polishing is carried out by usingan acid polishing agent with a pH value of 2.5 where silicon oxideparticles with a diameter of approximately 30 nanometers are dispersedin a pure water. A rotational speed of a polishing pad is maintained at50 times/min. A rotational speed of a polishing head is also maintainedat 50 times/min. The polishing agent is added at a rate of 75 cc/min.The polishing rate is approximately 0.4 micrometers/min.

As illustrated in FIG. 6F, a second photo-resist film, which is notillustrated, is applied on an entire surface of the device and thenpatterned to form a second photo-resist pattern which is not illustratedand positioned over the aluminum film 8-1 within the firstinterconnection grooves. An inter-layer insulator 13C with a thicknessof 0.8 micrometers is formed by using a plasma chemical vapor depositionmethod where the second photo-resist pattern is used as a mask. Thesecond photo-resist pattern, having apertures within which thefluoro-containing silicon oxide film 13C is formed, is removed by apeeling liquid so that via holes 15B are formed in the fluoro-containingsilicon oxide film 12.

As illustrated in FIG. 6G, a tungsten film 19 with a thickness ofapproximately 0.8 micrometers is selectively formed within the via holes51 B by a heat chemical vapor phase growth, in which WF₆ gas and SiH₄gas are used. The respective flow rates of WF₆ gas and SiH₄ gas are setat 20 sccm and 12 sccm. The substrate temperature is maintained at 270°C. The pressure of the reaction chamber is set at 4 Pa. The depositionrate is 0.6 micrometers/min.

As illustrated in FIG. 6H, a third photo-resist film is applied on anentire surface of the device and then patterned to selectively form athird photo-resist pattern, which is not illustrated and covers thetungsten film 19. A third fluoro-containing silicon oxide film 16A witha thickness of 0.8 micrometers is grown on the third fluoro-containingsilicon oxide film by using the third photo-resist pattern as a mask.The growth of the fluoro-containing silicon oxide film 16A is achievedby a liquid phase growth which uses a super-saturated hydrosilicofluoricacid solution, wherein the hydrosilicofluoric acid in the solution ismaintained in super-saturated state by immersing and dissolving analuminum piece in an aqueous solution which includes ahydrosilicofluoric acid at a concentration of about 40% by weight. Thereactions of hydrosilicofluoric acid with aluminum are expressed by theforegoing formulae (1) and (2). The reactions of hydrosilicofluoric acidwith aluminum, which are expressed by the above formulae (1) and (2),are caused by adding aluminum into the hydrosilicofluoric acid solution.The chemical equilibrium expressed in the left hand term is broken,thereby resulting in an extraction of fluoro-containing silicon oxide sothat the third fluoro-containing silicon oxide film 16A, which has Si-Fbonding, is deposited. During the deposition of the fluoro-containingsilicon oxide film 16A, the hydrosilicofluoric acid solution ismaintained at a temperature of 35° C. so that the solubility of aluminumto 1 liter of hydrosilicofluoric acid solution is set at approximately0.5 g/hour, thereby resulting in a fluoro-containing silicon oxide filmdeposition rate being in the range of 80 nanometers to 100 nanometers.

Subsequently, the third photo-resist pattern, having apertures withinwhich the fluoro-containing silicon oxide film 12 is formed, is removedby a peeling liquid so that third interconnection grooves 18A are formedin the third fluoro-containing silicon oxide film 16A.

A titanium film 6-3 with a thickness of 50 nanometers is deposited on anentire surface of the device by a sputtering method. A titanium nitridefilm 7-3 with a thickness of 100 nanometers is deposited on the titaniumfilm 6-3 by a sputtering method. An aluminum film 8-3 with a thicknessof approximately 0.7 micrometers is formed on the titanium nitride film7-3 by a thermal chemical vapor phase deposition, whereindimethylalminumlhydride AlH(CH₃)₂ is vaporized by a bubbling method witha carrier gas of hydrogen at a temperature of 30° C. and then introducedinto a reaction chamber. The flow rate of hydrogen gas used in thebubbling method is controlled at 250 sccm. The pressure of the reactionchamber is maintained at 130 Pa. The temperature of the substrate ismaintained at 250° C. The deposition rate of aluminum is approximately0.4 micrometers/min.

The aluminum film 8-3, the titanium nitride film 7-3 and the titaniumfilm 6-3 are selectively removed by a chemical/mechanical polishing toleave the aluminum film 8-3, the titanium nitride film 7-3 and thetitanium film 6-3 only within the third interconnection grooves 18A. Asa result, the second interconnections 9-3a, each of which comprises thealuminum film 8-3, the titanium nitride film 7-3 and the titanium film6-3, are formed in the second interconnection grooves 5A. The polishingis carried out by using an acid polishing agent with a pH value of 2.5where silicon oxide particles with a diameter of approximately 30nanometers are dispersed in a pure water. A rotational speed of apolishing pad is maintained at 50 times/min. A rotational speed of apolishing head is also maintained at 50 times/min. The polishing agentis added at a rate of 75 cc/min. The polishing rate is approximately 0.4micrometers/min.

The two level interconnection structure is fabricated. The surface ofthe inter-layer insulator between the two level interconnection layersare leveled. A sample is formed by use of the above technique, whereintell thousand via holes are connected in series to each other. Adiameter of the via holes is 0.6 micrometers. Each via hole has aresistance of approximately 0.8 Ω. The yield is over 93%.

According to the above method, the silicon oxide base film is formed tocover the first interconnections before the surface of the device isexposed to the super-saturated hydrosilicofluoric acid solution so thatthe first interconnections are free from any corrosion caused by thesuper-saturated hydro-silicofluoric acid solution. The tungsten filmwithin the via holes are also free from any corrosion caused by thesuper-saturated hydrosilicofluoric acid solution as being covered withthe photo-resist film. The combination of the chemical/mechanicalpolishing and subsequent liquid phase growth allows the inter-layerinsulator to have a level surface. The inter-layer insulator is formedwithout any liquid phase growtlh, thereby the process for forming theinter-layer insulator is relatively simple.

The above novel method for forming the multilevel interconnections isapplicable to three or more level interconnections. In place of thechemical/mechanical polishing method, an etch back process by a reactiveion-etching which uses a fluorine compound and/or a chlorine compound isalso available. The silicon oxide film may contain at least one ofphosphorus, boron and germanium. Such film may be formed by either asputtering method or a chemical vapor deposition method. Theinterconnections may be made of a conductive material which includes atleast one of titanium nitride, tungsten, molybdenum, gold, silver,copper, silicon, aluminum, titanium, titanium-conitainilig silicon. Suchconductive film may be formed by a chemical vapor deposition method or asputtering method.

The super-saturated hydrosilicofluoric acid solution may be prepared byheating a hydrosilicofluoric solution. The sniper-saturatedhydrosilicofluoric acid solution may also be prepared by dissolvingaluminum into a hydrosilicofluoric solution. The super-saturatedhydro-silicofluoric acid solution may be prepared by adding either aboric acid solution or water into a hydrosilicofluoric solution.

As described above, the interconnection grooves are formed by aselective growth of the fluoro-containing silicon oxide film withoutusing a reactive ion-etching process. This means that theinterconnection grooves are free from any variation in its size due toany variation in the size of a photo-resist pattern.

When the inter-layer insulator is formed, the first interconnectionswhich underlying the inter-layer insulator are not exposed to thesuper-saturated hydrosilicofluoric acid solution so that the firstinterconnections are free from any corrosion.

When the second fluoro-containing silicon oxide film which overlays theinter-layer insulator is formed, the conductive films in the via holesof the inter-layer insulator are not exposed to the super-saturatedhydrosilicofluioric acid solution so that the conductive films are freefrom any corrosion.

The grooves and the via holes are filled with the conductive material toobtain level surfaces for facilitating the planarization.

Whereas modifications of the present invention will no doubt be apparentto a person having ordinary skill in the art, to which the inventionpertains, it is to be understood that embodiments as shown and describedby way of illustrations are by no means intended to be considered in alimiting sense. Accordingly, it is to be intended to cover by claims allmodifications which fall within the spirit and scope of the presentinvention.

What is claimed is:
 1. A method for forming multilevel interconnectionsin a semiconductor device, comprising the sequential steps of:forming afirst silicon oxide film on a semiconductor substrate; forming a firstphoto-resist film pattern on the first silicon oxide film; exposing thesurface of the silicon oxide film not covered with the photo-resist filmpattern to a super-saturated hydrosilicofluoric acid solution toselectively deposit a first fluoro-containing silicon oxide film on thesilicon oxide film using the first photo-resist film pattern as a mask;removing the first photo-resist film pattern to form first grooves inthe fluoro-containing silicon oxide film; forming a first metal filmextending within said first grooves and over said firstfluoro-containing silicon oxide film; subjecting said first metal filmto a first chemical and mechanical polishing to leave said metal filmonly within said first grooves so that a remaining first metal film hasa top surface at a same level as a top surface of said firstfluoro-containing silicon oxide film to form a first flat top surface ofsaid substrate; forming a second silicon oxide film on the first flattop surface of device; said substrate; selectively forming a secondphoto-resist film pattern on said second silicon oxide film; exposing anentire surface of the device covered with the second photo-resist filmpattern to a super-saturated hydrosilicofluoric acid solution toselectively deposit a second fluoro-containing silicon oxide film on thesecond silicon oxide film using the second photo-resist film pattern asa mask; removing the second photo-resist film pattern to form secondgrooves in the second fluoro-containing silicon oxide film; removing thesecond silicon oxide film from within the second grooves; forming asecond metal film extending within said second grooves and over saidsecond fluoro-containing silicon oxide film; subjecting said secondmetal film to a second chemical and mechanical polishing to leave saidsecond metal film only within said second grooves so that a remainingsecond metal film has a top surface at a same level as a top surface ofsaid second fluoro-containing silicon oxide film to form a second flattop surface of said substrate; selectively forming a third photo-resistfilm pattern on said second fluoro-containing silicon oxide film;exposing an entire surface of the device covered with the thirdphoto-resist film pattern to a super-saturated hydrosilicofluoric acidsolution to selectively deposit a third fluoro-containing silicon oxidefilm on the second fluoro-containing silicon oxide film using the thirdphotoresist film pattern as a mask; removing the third photo-resist filmpattern to form third grooves in the third fluoro-containing siliconoxide film; forming a third metal film extending within said thirdgrooves and over said third fluoro-containing silicon oxide film; andsubjecting said third metal film to a third chemical and mechanicalpolishing to leave said third metal film only within said third groovesso that a remaining third metal film has a top surface at a same levelas a top surface of said third fluoro-containing silicon oxide film toform a third flat top surface of said substrate.
 2. The method asclaimed in claim 1, wherein during the steps of forming of the first,second and third fluoro-containing silicon oxide films, thehydrosilicofluoric acid solution is maintained at a temperature of 35°C. so that the solubility of aluminum to 1 liter of hydrosilicofluoricacid solution is set at approximately 0.5 g/hour.
 3. The method asclaimed in claim 1, further comprising the step of:forming a base filmmainly containing silicon oxide on the entire surface of the deviceprior to the formation of the second photo-resist film.
 4. The method asclaimed in claim 1, wherein the step for forming the first, second, andthird metal films comprises the following steps of:forming a titaniumfilm on an entire surface of the device by sputtering; forming atitanium nitride film on the titanium film by sputtering; forming analuminum film on the titanium nitride film by a thermal chemical vaporphase deposition carried out by the following steps of: vaporizingdimethylaluminumhydride AlH(CH₃)₂ by a bubbling method with a carriergas of hydrogen at a temperature of 30° C.; and introducing thevaporized dimethylaluminumhydride AlH(CH₃)₂ into a reaction chamber,where a flow rate of hydrogen gas is controlled at 250 sccm, atemperature of the substrate is maintained at 250° C. and a pressure ofthe reaction chamber is 130 Pa.